Diffuse Idiopathic Skeletal Hyperostosis

Etiology

Recent studies have found a significant association between DISH and metabolic disorders, such as diabetes mellitus, hyperinsulinemia, obesity, dyslipidemia, and hyperuricemia.[6][7][8] While these clinical associations are noted in the literature, the pathogenesis and mechanisms behind the characteristic ossification patterns of DISH remain debated. Some researchers have suggested potential causes, including mechanical stress and strain, exposure to various toxic factors, and genetic contributions.[1]

Angiogenesis has also emerged as a key area of investigation, suggesting a potential pathophysiologic link to various clinical manifestations of DISH, which are more commonly seen in patients with metabolic syndrome. For instance, carotid atherosclerosis and DISH are more frequently observed in these patients. Additionally, higher prevalence rates of aortic valve sclerosis have been identified as an independent risk factor for cardiovascular events in individuals with DISH.[9]

Epidemiology

The epidemiology of DISH has been relatively underexplored, with few publications on the subject.[10] DISH is rarely reported in patients aged 50 or younger.[2] The overall incidence in the general population ranges from 6% to 12%. Among individuals aged 50 or older, DISH affects approximately 25% of males and 15% of females. Prevalence rates increase in patients aged 80 or older, with 28% males and 26% females affected. Current theories suggest that the disease begins between the third and fifth decades of life, but clinical symptoms typically manifest later.[2]

An autopsy study found evidence of DISH in approximately one-fourth of specimens, with a mean age of 65 (minimum age 50).[11] Population-based studies have reported an overall prevalence rate of 2.5% to 28%, with higher rates associated with increasing age and a gender predisposition favoring males over females for DISH.[12][13][14][15] Additionally, DISH may be more common in the White population compared to Black, Asian, and Native-American populations.[14]

A 2016 study from Japan reported a discrepancy in DISH prevalence rates between diagnoses made using computed tomography (CT) scans and those based on radiographic imaging alone. The prevalence in the general population was 17.6% based on radiographs and 27.2% based on CT imaging.[16]

Pathophysiology

DISH in the spine most commonly affects the right side of the thoracic region and is less frequently observed in the cervical spine.[17] The literature supports the original theory that the pulsatile descending aorta serves as a protective mechanical barrier, preventing DISH formation on the contralateral (left) side of the thoracic spine.[2] Moreover, recent studies have also shown that DISH presenting in the cervical and lumbar regions of the spine exhibits distinctly different ossification patterns. 

A study conducted in 2017 found that newly formed bone in the cervical spine primarily occurred anterior to the vertebral bodies, contrasting with the anterolateral bone deposition pattern typically seen in DISH of the thoracic spine.[18] A plausible pathophysiological explanation for these varying ossification patterns involves the regional arterial anatomy. The pulsatile protective mechanical barrier theory is further supported by studies showing that patients with situs inversus develop DISH on the left side of the thoracic spine.[19] Finally, studies of DISH in the cervical and lumbar spine have reported symmetrical, nonmarginal syndesmophyte ossification patterns.

DISH can cause pain from nerve impingement or bony growths, leading to acute monoarticular synovitis, limited spinal range of motion, dysphagia, polyarticular pain, spinal or extremity pain, and an increased risk of unstable spine fractures.[20] The intervertebral ossification associated with DISH progresses with age. Although the presence of DISH is a risk factor for vertebral fragility fractures, increasing age and ossification may, paradoxically, provide some protection against these fractures.[21]

History and Physical

Patients with DISH are often asymptomatic, with the condition typically discovered incidentally. However, neuropathy or bony overgrowth causing physical impingement may lead to pain.[20] The traditional diagnostic criteria for DISH include 3 key elements, as outlined below.[3]

• The presence of flowing ossifications that involves a minimum of 4 contiguous vertebrae.
• Preservation of disc height with minimal or no significant degenerative changes in the affected vertebral segments, distinguishing DISH from degenerative spondylosis.
• Absence of ankylosis at the facet-joint interface and no sacroiliac (SI) joint erosion, sclerosis, or fusion, differentiating DISH from ankylosing spondylitis. 

Please see StatPearls' companion resources, "Lumbar Spondylolysis and Spondylolisthesis," "Lumbar Degenerative Disk Disease," and "Rheumatoid Arthritis and Ankylosing Spondylitis," for more information.

The current widespread definition of DISH by Resnick and Niwayama has recently been challenged, as its inclusion criteria may better apply to advanced stages of the condition.[22] As early as 1985, Utsinger questioned the prevailing definition and proposed lowering the threshold for spinal involvement to two contiguous vertebrae, while also incorporating peripheral enthesopathies.[23]

Recent challenges have raised concerns about the validity and consensus surrounding the evolving criteria for diagnosing DISH. A 2013 Delphi exercise revealed that consensus and definitive literature support may only exist for the following elements:

• Presence of exuberant new bone formation in the characteristic locations.
• Presence of enlarged bony bridges in the cervical, thoracic, or lumbar spine.

Differentiating Diffuse Idiopathic Skeletal Hyperostosis From Ankylosing Spondylitis

Healthcare providers often face challenges in differentiating DISH from ankylosing spondylitis. Key distinguishing features between the 2 conditions include the following elements:[24][25]

• An older age of presentation favors DISH over ankylosing spondylitis.
• The absence of SI joint erosions supports a diagnosis of DISH rather than ankylosing spondylitis.
  • Recognizing the clinical overlap in milder cases of SI joint pathology is important, as SI osteophytes have been observed in patients with DISH.
• The absence of apophyseal joint obliteration favors DISH over ankylosing spondylitis.
• Frequent ossification of the anterior longitudinal ligament is characteristic of DISH.
• The absence of enthesopathy with erosions favors DISH over ankylosing spondylitis.
• Lack of association with HLA-B27 favors DISH over ankylosing spondylitis.
• DISH is generally a milder condition compared to ankylosing spondylitis and may even present without pain.
  • Clinical symptoms of DISH tend to be minimal, contrasting with the extensive findings observed on radiographs or advanced imaging.
  • In many cases, DISH is discovered incidentally in asymptomatic patients.

Despite the ongoing debate over diagnostic criteria, the classic clinical presentation of DISH typically involves an older patient experiencing increasing back pain and stiffness. Soft tissue involvement, particularly from osteophytes in the cervical segments, can lead to dysphagia, hoarseness, sleep apnea, and difficulties with intubation.[26][27] Further evaluation may include a swallow study or consultation with otolaryngology or gastroenterology. Additionally, heightened clinical suspicion is recommended for older patients presenting with acute-on-chronic back pain, especially in the context of minor trauma.

As with any condition involving contiguous osseous fusion of vertebral and spinal elements, DISH creates a longer lever arm in the spine, increasing the risk of fractures.[28] Therefore, performing a comprehensive neurovascular examination and imaging of the entire spine is essential for all patients to minimize the risk of overlooking fractures in adjacent spinal regions.

Peripheral joint involvement in DISH has the following distinctive features:

• Joints typically unaffected by primary osteoarthritis, such as the hip and knee, are commonly involved.
  • Foot and ankle involvement has been reported in up to 70% of patients.
    • Clinical and radiographic findings often show heel spurs, Achilles tendinitis, and plantar fasciitis.
• Hypertrophic changes are more pronounced compared to primary osteoarthritis.
• Prominent enthesopathy is observed adjacent to peripheral joints.
• Calcification and ossification of entheses occur at sites other than the joints.[29]

Peripheral findings in DISH often include hyperostosis and tendonitis.[29] Enthesophytes may be present in the pelvis, affecting the iliac wing and ischial tuberosity.[30] Periarticular hyperostosis and tendinous ossifications have also been reported in the hip, knee, shoulder, elbow, hand, and wrist.[2]

Evaluation

Laboratory values such as erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor, and antinuclear antibody are typically normal in DISH. Radiographic evaluation using anteroposterior and lateral spine imaging often reveals the hallmark "flowing candle wax" appearance. This refers to non-marginal syndesmophytes projecting horizontally from the vertebrae, leading to extra-articular ankylosis. This radiographic feature differs significantly from the vertical "bamboo spine" observed in ankylosing spondylitis, which results from intra-articular disc space ossification.[2] Despite these distinctions, degenerative and inflammatory features on diagnostic imaging can overlap with other conditions, such as degenerative disc disease and spondyloarthritis.[31] Radiographic definitions of new bone formation have been developed to improve the accuracy of diagnosing and differentiating DISH from other spinal pathologies.[32]

Increased radiodensity and preservation of facet joints and disc spaces on spine imaging are key features that help differentiate DISH from ankylosing spondylitis, which is often associated with osteopenia and degenerative changes.[2] The relationship between DISH and low bone density remains a topic of debate in the literature.[33] However, a potential clinical association suggests an elevated risk of vertebral fractures, particularly following low-energy trauma. 

While patients with osteoporosis may experience vertebral compression fractures from minimal activities, such as lying in bed in a nursing home,[34][35] vertebral fractures in patients with DISH have also been reported following elective, unrelated surgical procedures. For example, a 2012 case report described a patient with DISH who developed postoperative incomplete paraplegia following a routine total hip replacement.[36] Please see StatPearls' companion resources, "Osteoporosis in Spinal Cord Injuries," "Osteopenia," and "Osteoporosis," for more information.

As the thoracic spine is most commonly affected in DISH, clinicians should have a low threshold for ordering thoracic spine or chest radiographs, even in patients presenting with primary neck or low back pain, stiffness, or diffuse extremity complaints.[37] Diagnosing DISH through thoracic imaging can help avoid unnecessary diagnostic workups and surgical procedures.

Technetium bone scans may show increased uptake in regions affected by DISH; however, this finding can mimic metastatic disease and is typically not useful in nontraumatic scenarios.[38] Radiographic evaluation of the lumbar spine and pelvis is essential, as the presence of SI joint pathology could shift the diagnostic focus toward other conditions, such as seronegative spondyloarthropathies.

Minor trauma in patients with DISH can lead to fractures and instability, which are often overlooked and may result in neurologic compromise and delayed treatment. Occult fractures in these patients necessitate a comprehensive evaluation using advanced imaging modalities, such as CT, MRI, or CT myelogram.[39] Extraspinal complaints in patients with DISH should be properly assessed, typically starting with plain radiographs.

Treatment / Management

For most patients with isolated back discomfort due to DISH, primary treatment options include activity modification, physical therapy, bracing, nonsteroidal anti-inflammatory drugs (NSAIDs), and bisphosphonates.[2] These interventions aim to alleviate symptoms, improve mobility, and prevent further complications associated with the condition.

Surgical decompression and stabilization may be indicated for specific sequelae of DISH, such as fractures, cervical myelopathy, lumbar stenosis, neurologic deficits, infections, or painful deformities. Early intervention is essential to prevent symptom progression and improve overall outcomes.

Differential Diagnosis

The differential diagnoses for patients presenting with back pain, stiffness, and spondylophytosis include, but are not limited to, the following conditions:[40]

• Ankylosing spondylitis
• Spondylosis deformans (differentiated from DISH by the lack of association with thoracic anterior longitudinal ligament ossification)
• Seronegative spondyloarthropathies
• Charcot spine
• Acromegaly
• Psoriasis
• Reactive arthritis
• Pseudogout
• Hypoparathyroidism

Treatment Planning

Recent evidence suggests that growth factors may have a role in targeting sites of new bone growth at the entheses in patients with DISH.[41] These factors could provide potential therapeutic options for modulating ossification and alleviating symptoms associated with the condition.

Prognosis

The prognosis of DISH varies based on the severity of the condition and the symptoms experienced by the individual. While DISH is a progressive disorder, it typically advances slowly. Most individuals can manage their symptoms with conservative treatments, such as physical therapy, pain management, and maintaining an active lifestyle to preserve range of motion. However, in some cases, DISH can lead to significant complications, including severe spinal stiffness, nerve compression, and difficulties with swallowing or breathing if calcification extends to the cervical or thoracic regions.

Rarely, surgical intervention may be necessary to relieve compression or correct severe deformities. Overall, while DISH can affect quality of life, especially in advanced stages, it is not typically life-threatening. With proper management, many patients are able to maintain a functional level of mobility.

Complications

Patients with DISH who experience spinal fractures are at greater risk of instability due to ligamentous calcification and increased deforming forces from vertebral ankylosis. In these cases, longer instrumentation is often necessary to account for the lever arms acting on the fracture site.

Meyer demonstrated that surgical treatment of cervical fractures in older patients with DISH correlates with a 15% mortality rate, compared to 67% with conservative treatment. This emphasizes the importance of prompt diagnosis, evaluation, and intervention following trauma in patients with DISH.[15]

Heterotopic ossification is a common complication following total hip arthroplasty in patients with DISH, occurring in 30% to 56% of cases.[42][43] In contrast, patients without DISH in the cited studies had a much lower rate of heterotopic ossification, ranging from 10% to 22%.[42][43] Fahrer et al reported low rates of pain and functional limitations in patients with DISH after total hip arthroplasty and recommended against routine prophylaxis for heterotopic ossification in these patients.[43]